The present disclosure relates to the biosynthesis of bacterial extracellular galactomannan polysaccharides and subunits thereof for use in subterranean formation operations. More particularly, the present disclosure relates to preparation of an extracellular galactomannan polysaccharide derived from mannose and galactose monosaccharides for use in subterranean formation operations.
Treatment fluids may be used in a variety of subterranean formation operations including, drilling operations, stimulation operations, sand control operations, and the like. Subterranean operations often require the use of treatment fluids that are sufficiently viscous to suspend solids, such as drill cuttings, proppant, gravel, and the like. For example, stimulation operations, such as hydraulic fracturing, typically require the use of viscosified treatment fluids in order to maintain proppant suspension for placement in fractures. By keeping the fracture from fully closing, the proppants aid in forming conductive paths to allow produced fluids, such as hydrocarbons, to flow. Similarly, sand control operations typically require the use of viscous treatment fluids to carry gravel particulates downhole to a particular location, usually between a gravel pack screen to prevent the transport of sand or other unconsolidated particles with produced fluids. The gravel particulates create a physical barrier to the transport of the sand or unconsolidated particulates. Failure of the treatment fluid to suspend the gravel particulates (i.e., maintain sufficient viscosity) could result in the deposition of the gravel particulates in an undesired location, thus frustrating the purpose of the treatment fluids.
To obtain the necessary viscosity to carry particulates, gelling agents are commonly used to viscosify treatment fluids. Such gelling agents are generally polymeric materials such as, for example, galactomannans, cellulose derivatives, and biopolymers. Galactomannans, polysaccharides comprised of the monosaccharide subunits mannose and galactose, are often preferred gelling agents because they are relatively inexpensive and exhibit high efficiency and performance in subterranean formation operations because they can be used effectively at relatively low concentrations with crosslinking agents to form high yield point fluids that can support and transport particulates (e.g., cutting particulates, proppant particulates, gravel particulates, and the like). Additionally, they can add sufficient viscosity to provide high flow viscosity fluids that are capable of fracturing oil bearing subterranean formations.
Galactomannans serve as storage carbohydrates that accumulate in the endosperm of seeds of leguminous plants (e.g., fenugreek plants (Trigonella foenum-graecum), guar bean plants (Cyamopsis tetragonoloba), tara plants (Caesalpinia spinosa), locust bean plants (Ceratonia siliqua)). Galactomannans are polysaccharides consisting of a (1→4)-linked β-D-mannopyranose backbone with branchpoints from their 6-positions linked to α-D-galactose (1→6)-linked α-D-galactopyranose). Because galactomannans are produced in plants, their supply for use in treatment fluids in subterranean formation operations may be limited by the natural life cycle of the plants and related farming limitations (e.g., seasonal fluctuations, land availability, biological variability, and the like). Their supply may be further limited by global economic conditions and normal supply and demand fluctuations. Therefore, a method of producing commercial quantities of galactommanan for use in subterranean treatment operations that is renewable and season independent may be of benefit to one of ordinary skill in the art.